JP2006243120A - Developing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of forming an image of good quality free of an image blur, developer clogging, etc., by suppressing white dotting due to a development leak (discharge of a developing bias) in magnetic brush system development using a two-component developer. <P>SOLUTION: The image forming apparatus has a developer carrier in which a plurality of magnetic electrodes are fixed and an image carrier which is developed on a counter basis by the developer carrier and is characterized in that the magnetic electrode arrangement in the developer carrier meets a condition of 0.19≤θ1/θ2≤0.37, where θ2 is the inter-electrode angle between a developing electrode peak and a conveying electrode peak and θ1 is the angle that the position where the developer carrier and image carrier are closest to each other and the developing electrode peak form. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a developing device. In particular, the present invention relates to a developing device that performs magnetic brush development using a two-component developer on an electrostatic latent image.

  As a developing method in an image forming apparatus, magnetic brush development using a two-component developer in which toner and a magnetic carrier are mixed is often used. This magnetic brush developing system uses a developing roller containing a magnetic pole as a developer carrying member, and rotates the surface cylindrical portion of the developing roller called a developing sleeve to attract and convey the developer magnetically, The developer sleeve is formed on the surface of the developing sleeve, and the surface of the photosensitive member as an image bearing member rotating relative to the developing roller is rubbed with the developer spike (referred to as a magnetic brush) to thereby rub the photosensitive member. The toner is electrostatically moved to the upper electrostatic latent image and developed.

  There are a plurality of magnetic poles included and fixed to the developing roller. As the magnetic carrier in the developer is transported on the surface of the developing sleeve, a spike with a continuous carrier stands at the position where the magnetic pole exists (referred to as the top). Until the position where the magnetic pole is located (referred to as “between the poles”), the shape of the carrier's ears is repeated. After the toner mixed with the carrier moves to the photosensitive member and the toner is low, the magnetic brush returns to the developer supply tank and once peels off. Then, a new toner-rich developer forms a magnetic brush. Repeat that.

  This magnetic brush development mechanism can effectively control the toner transfer to the photoreceptor by using a magnetic brush, and the toner itself needs to be magnetized because the brush is formed using a magnetic carrier. It is frequently used because it is not available, but there are various variations in its usage.

  For example, with respect to the developer transport direction, the developer is transported in a direction in which the developing roller is rotated so that the developer is transported in a direction along the rotation direction of the photoconductor, or in the direction opposite to the rotation direction of the photoconductor. There is a counter system that rotates the developing roller.

  Although depending on the peripheral speed ratio between the photoconductor and the developing roller, generally, in the latter, more magnetic brushes rub against the photoconductor than in the former, so that development efficiency is good. On the other hand, since the carrier-rich magnetic brush after toner development often rubs the photoconductor, the developing bias applied to the developing sleeve during development is easily discharged to the photoconductor through the magnetic brush, and the toner locally. White spots may occur.

  As for the developer transport method, the developing sleeve is fixed, the magnet body provided with a plurality of magnetic poles in the circumferential direction is rotated, the developing sleeve and the magnet body are both rotated, and the developing sleeve is There is a method of rotating and fixing the magnetic pole inside. Among the former, the magnet body itself rotates, so the magnetic brush ears stand and lie down, and move while repeating undulations. Unevenness in the developer transport amount affects development. Although there is an advantage that it is difficult, there are a load and vibration for rotating the magnet body at high speed, and a difficulty in terms of the apparatus. The latter does not have such a problem because the magnet body is fixed, but even if the developer moves due to the rotation of the developing sleeve, the wavy undulations of the magnetic brush caused by the magnetic poles inside are located on the sleeve. The unevenness of the developer transport amount tends to affect the development. For these reasons, the arrangement of the magnetic poles in the circumferential direction of the magnet body has a great influence on the developing state, and it is necessary to pay attention when adopting a method of fixing the magnetic poles.

  Conventionally, the position where the developing roller as the developer carrying member is closest to the photosensitive member as the image carrying member, that is, the developing position is made to coincide with the position of the magnetic pole included in the developing roller. This is called best development. This merit is that at the position of the magnetic pole (referred to as the developing pole), the surface of the photoconductor is rubbed with the magnetic brush standing up, and a sufficient amount of toner can be supplied to the photoconductor. It is difficult to adversely affect image density due to lack of developer. In other words, the best development can make the most of the benefits of magnetic brush development. In order to take advantage of such merits, it is desirable to carry out the counter-type developer conveyance described above.

  However, there are problems with these counter systems and superb development. Depending on the characteristics of the carrier, the strength of the magnetic force, the unevenness of the transport amount, etc., the heading state (length, thickness, density, etc.) fluctuates, and the development bias tends to be discharged to the photoreceptor through the magnetic brush during development. There are problems that white spots without toner are locally generated or that the developer is easily clogged on the upstream side of the developer conveyance. This is particularly a problem when using a high magnetic force carrier.

  On the other hand, the position at which the developing roller as the developer carrying member is closest to the photosensitive member as the image carrying member, that is, the developing position, is not the position of the magnetic pole included in the developing roller, for example, between the magnetic pole and the next magnetic pole. A system (called inter-electrode development) located between them has also been proposed. Since the head of the magnetic brush is lying between the magnetic poles, clogging of the developer is less likely to occur. In addition, the fact that the ears are sleeping is less likely to discharge to the photoreceptor side through the brush of the carrier.

  However, conversely, this means sacrificing the merit of superb development, that is, the merit of magnetic brush development in a sense, and there is a problem in terms of stable development, that is, securing image density.

  Patent Document 1 proposes an inter-electrode development using the with method. This limits the development position so that the deviation between the magnetic pole and the magnetic pole is within 1/10 of the angle between the poles. However, this aims at developing the magnetic brush in a non-contact manner with the photoconductor, and has problems of stability of non-contact development and prevention of carrier adhesion rather than discharge phenomenon and developer clogging. Accordingly, although it is estimated that there is a certain effect as a countermeasure against the discharge phenomenon (leakage) and the developer clogging, the disadvantages in the extreme development such as image density maintenance and density unevenness are rather increased.

  Japanese Patent Application Laid-Open No. 2004-228561 proposes inter-electrode development using a counter method. Although the development position is also set to be between the magnetic pole and the magnetic pole, it is premised that the magnetic brush is developed in a non-contact manner with the photoreceptor, and the development bias waveform is characterized in order to have an effect on the development image quality. ing. Therefore, although it is estimated that this also has a certain effect as a measure against the discharge phenomenon (leak) and developer clogging, the disadvantages of the extreme development such as image density retention and density unevenness are rather increased.

  Patent Document 3 also proposes the inter-electrode development with the width method. This is because the magnetic brush is not brought into contact with the photoconductor side on the downstream side in the rotation direction of the photoconductor, resulting in inter-electrode development. The purpose is to prevent blurring of horizontal fine lines and white-out of the trailing edge, and to prevent the cleaning effect of the toner adhered to the photoconductor by the magnetic brush. Therefore, it is insufficient as a countermeasure against the discharge phenomenon and the developer clogging, and also has a disadvantage in the extreme development such as image density maintenance and density unevenness.

From the standpoint of image density retention and density unevenness, the counter method and superb development are desirable in view of the essence of magnetic brush contact development. Some ideas have been desired as countermeasures against developer clogging.
Japanese Patent Laid-Open No. 6-149063 JP 2000-66494 A JP 2000-305361 A

  As described above, in the case of magnetic brush system development, counter system and superb development are desirable in terms of image quality (density, blurring, unevenness), but there are problems of white spots due to discharge and clogging of developer. In particular, when a small-diameter developing roller and a high magnetic force carrier are used, white spots are likely to occur due to development leakage (development bias discharge, hereinafter also referred to as leakage). Further, the developer is likely to be clogged upstream in the developer transport direction.

  An object of the present invention is to appropriately form a plurality of magnetic poles contained in a developer carrier, thereby suppressing the occurrence of the white spot image and forming a high-quality image free from image blur and developer clogging. It is an object of the present invention to provide an image forming apparatus capable of performing the above.

  In order to solve the above problems, the developing device of the present invention has the following characteristics.

(Claim 1)
In a developing device that forms a toner image on an image carrier by developing the electrostatic latent image formed on the surface of the image carrier with a two-component developer containing toner and a magnetic material.
A developer carrier for carrying and transporting a two-component developer in a direction opposite to the moving direction of the image carrier;
A developer pole which is encapsulated and fixed to the developer carrier and forms a magnetic brush so that the two-component developer on the developer carrier rubs the surface of the image carrier; A plurality of magnetic poles including a transport pole for transporting the two-component developer to the development pole,
The developing device according to claim 1, wherein the arrangement of the magnetic poles satisfies the following conditions (1), (2), and (3).
(1) The magnetic flux density peak in the normal direction of the developing pole is arranged at a downstream side of 10 ° or more and 20 ° or less with respect to the developer transport direction from the closest position between the developer carrying member and the image carrier.
(2) The magnetic flux density peak in the normal direction of the transport pole is arranged upstream of the closest position.
(3) 0.19 ≦ θ1 / θ2 ≦ 0.37, where θ2 is the angle between the development pole peak and the transport pole peak, and θ1 is the angle between the closest position and the development pole peak. .

(Claim 2)
2. The developing device according to claim 1, wherein a magnetic attraction force of the developer carrier at a position closest to the developer carrier and the image carrier is 0.27 N or more.

  According to the first aspect of the present invention, the magnetic pole included in the developer carrying member (developing roller) is appropriately arranged so that the closest position (developing position) between the image carrying member (photosensitive member) and the developer carrying member. ) Can be appropriately controlled, an image forming apparatus that can suppress a white spot image due to leakage and can form a high-quality image without image blur or density reduction can be provided.

  According to the second aspect of the present invention, in addition to the above, further development is achieved by appropriately setting the magnetic attraction force of the developer carrier at the closest position between the developer carrier and the image carrier. It is possible to provide an image forming apparatus in which agent clogging is unlikely to occur.

(overall structure)
FIG. 1 is a schematic sectional view showing an embodiment of an image forming apparatus according to the present invention. The configuration and arrangement of the image forming apparatus will be described with reference to FIG.

  A primary transfer belt 14 is disposed in the center of the apparatus. Below the primary transfer belt 14, four imaging cartridges 17 for Y (yellow), M (magenta), C (cyan), and K (black) and the respective reproduction colors are arranged. This is a so-called tandem system. Below each imaging cartridge 17, four exposure devices 18 are arranged for exposing on a photoreceptor included in the imaging cartridge and forming a latent image.

  A secondary transfer roller 12 is disposed on the right side of the primary transfer belt 14. Above the secondary transfer roller 12, a fixing unit 11 for fixing the recording sheet secondarily transferred by the secondary transfer roller is disposed.

  Above the primary transfer belt 14, four toner cartridges 13 containing Y (yellow), M (magenta), C (cyan), K (black), and replenishment toners for respective reproduction colors are included. These are arranged in the same order as the imaging cartridge 17.

  A cleaner unit 15 is disposed on the left side of the primary transfer belt 14. Below the cleaner unit 15 is disposed a waste toner box 16 for collecting and storing the residual toner collected by the cleaner unit.

(Imaging unit configuration)
FIG. 2 is a schematic cross-sectional view of the imaging cartridge 17 in FIG. The configuration and arrangement of the imaging cartridge 17 will be described with reference to FIG. The imaging cartridges for Y, M, C, and K reproduction colors have the same configuration except for the reproduction color of the toner contained in the built-in developer. Therefore, in the following description, one imaging cartridge is used. Only 17 will be described.

  The imaging cartridge 17 includes a developing unit 19 and a photosensitive drum unit 20 arranged as shown in FIG.

(Photosensitive drum unit configuration)
The main components of the photoconductor drum unit 20 are a photoconductor 1 which is an image carrier for forming a latent image, a charging device 3 for charging the photoconductor, and cleaning of residual toner after development and transfer of the photoconductor. And cleaner 2 to be used.

(Development unit configuration)
The main components of the developing unit 19 as a developing device are a developer tank 22 filled with a developer (not shown) composed of toner and a carrier, and agitation of the developer with new toner replenished from the toner cartridge 13. A stirring screw 9, a supply screw 8 that conveys and supplies the stirred developer, and a developing roller 4 that is a developer carrying member that develops the photoreceptor 1 with the supplied developer.

(Image formation process)
Next, an example of an image forming process according to the present invention will be described with reference to FIGS.

  In the photosensitive drum unit 20, the charging device 3 charges the surface of the rotating photosensitive member 1 to form a predetermined surface potential. As the photosensitive member 1 rotates, the exposure device 18 starts exposure of an image pattern on the photosensitive member 1 to form an electrostatic latent image. Next, a predetermined developing bias is applied to the developing roller 4 provided in the developing unit 19, and the latent image on the photosensitive member 1 is developed with toner as described below to form a toner image.

  In the developing unit 19, there is a developer (not shown) composed of sufficiently agitated toner and carrier in the developing tank 22, and the developer is supplied to the developing roller 4 by the supply screw 8 and rotates. Thus, the magnetic brush is formed and conveyed to a position close to the photoreceptor 1 (development position). The magnetic brush on the rotating developing roller 4 develops the electrostatic latent image on the photosensitive member 1 with toner by rubbing the surface of the rotating photosensitive member 1 and transferring the toner.

  The magnetic brush that has consumed the toner is conveyed and returned to the developing tank 22. The developer in the developer tank is replenished with new toner as much as the toner is consumed. New toner replenished from the toner cartridge 13 is sufficiently agitated with the developer by the agitating screw 9 and is supplied to the supply screw 8 separated by a partition from a developing tank communicating portion (not shown) on the front side or the rear side in the axial direction. It is sent.

  On the other hand, the toner image developed on the surface of the photoreceptor 1 is transferred to the primary transfer belt 14 conveyed in synchronization. After the transfer of the toner image, the photoreceptor 1 is scraped off the transfer residual toner by the cleaner 2, and then returns to a state where it can be charged by the charging device 3 again through a process such as charge removal if necessary.

  The above-described process in the imaging cartridge 17 is the transfer position on the primary transfer belt 14 for four imaging cartridges 17 for Y (yellow), M (magenta), C (cyan), and K (black), and the respective reproduction colors. Is repeated while synchronizing, and the color toner image in which the four color toner images are superimposed is transferred onto the primary transfer belt.

  The color toner image on the primary transfer belt 14 is transferred to a transfer recording material (not shown) fed at the position where it contacts the secondary transfer roller 12 in accordance with the movement and timing of the primary transfer belt. Is done. The secondary transfer residual toner on the primary transfer belt 14 is collected by the cleaner unit 15, and the primary transfer belt returns again to a state in which primary transfer from the imaging cartridges 17 of each color is possible.

  On the other hand, the transfer recording material on which the color toner image is secondarily transferred is conveyed to the fixing unit 11 as it is. The color toner image is fixed on the recording material by the fixing unit, and the recording material is discharged. Thereby, the image formation of one image is completed. If necessary, these processes will be repeated.

(About magnetic pole arrangement)
FIG. 3 is an enlarged schematic cross-sectional view showing a state in which the photosensitive member 1 of the photosensitive drum unit 20 is developed by the developing roller 4 of the developing unit 19 in FIG. With reference to FIG. 3, conditions relating to development of the photoreceptor 1 by the developing roller 4 will be described.

  The magnetic pole included in the developing roller is fixed, and the developing sleeve is rotated to transport the developer. Basically, the counter development method is used to perform the interelectrode development. However, although the development is between the poles, the arrangement of the magnetic poles has the following characteristics as compared with the prior art.

  In FIG. 3, 1 is a photosensitive member, 4 is a developing roller, 5 is a regulating plate for regulating the developer layer, and 6 is a developing member for stabilizing the function of the regulating plate. An arrow A shown in the photoconductor 1 indicates the rotation direction of the photoconductor. An arrow B in the developing roller 4 indicates the rotating direction of the developing sleeve, that is, the developer conveying direction.

  In the developing roller 4, the magnetic pole arrangement by the magnet fixed inside is shown by a normal direction magnetic flux density pattern. FIG. 4 shows an enlarged view of the magnetic flux density pattern in the normal direction.

  The magnetic poles in the developing roller 4 consist of five poles, and the magnetic poles called N1, S1, N2, S2, and S3 are arranged as shown in FIG. 3 or FIG. S <b> 2 is called a catch pole and receives the developer from the lower supply screw 8. N2 is called a regulation pole, and has a smooth magnetic flux density and a unique shape in order to stably regulate the conveyance amount on the developing roller. The bend returning member 6 including the bend facing the N2 pole is also attached to stabilize the regulation of the conveyance amount. Similarly, in order to regulate the layer thickness of the developer on the developing roller 4, the regulating plate 5 is attached as a member facing the N2 pole, and the surface of the developing roller 4 and the regulating plate 5 are set at a predetermined interval Db. Yes.

  S1 is called a conveyance pole, and conveys the regulated developer to the subsequent N1 pole. N1 is called a developing pole and is a magnetic pole that contributes to development and has a magnetic flux density stronger than the other poles. S3 is called a sealing electrode, and the developer is conveyed while being sealed so as to prevent the developer from leaking from the developing tank and prevent the toner from scattering. The area between the S2 and S3 poles is called a peeling pole, and has a function of peeling off the developer consumed by the toner from the developing roller 4 at the depolarizing portion. In addition, it also functions to replace the developer that has consumed toner with a new developer.

  Each of θ1 and θ2 shown in FIG. 3 represents a circumferential angle around the shaft 41 of the developing roller 4. θ1 is an angle formed by the peak position of the magnetic flux density in the normal direction of the N1 pole, that is, the developing pole, and the position where the developing roller 4 is closest to the photoreceptor 1, that is, the developing position. Similarly, θ2 is an angle formed between the peak position of the normal direction magnetic flux density of the N1 pole, that is, the development pole, and the peak position of the normal direction magnetic flux density of the S1 pole, that is, the transport pole.

  In the embodiment of the present invention, the peak position of the magnetic flux density in the normal direction of the N1 pole, that is, the developing pole is set downstream in the developer transport direction at the position P where the developing roller 4 is closest to the photosensitive member 1. The angle θ1 formed is arranged so as to be within a range of 10 ° to 20 °. Further, the magnetic pole arrangement of the N1 pole and the S1 pole is set so that the ratio of θ1 and θ2 is taken and the condition of 0.19 ≦ θ1 / θ2 ≦ 0.37 is satisfied. In addition, it is desirable that the magnetic attractive force at the position P where the developing roller 4 is closest to the photosensitive member 1 is 0.27 N or more, and this is performed.

  Conventionally, as described above, in order to take advantage of the characteristics of magnetic brush development, development is performed on the N1 pole, that is, on the development pole, that is, the magnetic pole position is made to coincide with the closest position of the developing roller 4 and the photoreceptor 1 (θ1≈0 °). ) Was done. These are good in terms of image density in consideration of the effect on image quality due to development, but have problems such as white spots due to electric discharge and clogging of developer. Also, although it is considered to be a technique such as extreme development, many of them have different purposes and do not solve the above problems sufficiently, or conversely cause side effects such as blurring and unevenness of image density Met.

  In the present invention, the interrelationship of the state of the magnetic brush (how to stand the ear, density, thickness, length, strength, transport amount, transport speed) is related to the influence on the above-mentioned developed image. It found a solution to control through magnetic pole arrangement. In particular, the arrangement of magnetic poles is dominant in the state of the ear, and the above-described form is set centering on this.

  The operation of the magnetic pole arrangement of the developing roller according to the present invention will be described.

(White spots due to leaks)
In the magnetic pole arrangement described above, when θ1 is 10 ° or more and 0.19 ≦ θ1 / θ2 as in the present invention, white spots due to leakage do not occur, but θ1 is 10 ° or less, or θ1 / θ2 < In the case of 0.19, generation of white spots due to leakage is observed. The reason for this is presumed to be that the occurrence of white spots depends on the state of the ears of the magnetic brush at the development position.

  In the present invention, the state of the spike is controlled with the magnetic brush standing, and specifically, by adjusting the relative position (θ1 / θ2) between the transport pole and the developing pole, It was possible to tilt the brush toward the upstream side of the conveying direction while raising the brush head. By controlling the state of the spike in this way, it was possible to bring an essential difference in the occurrence of vitiligo spots.

(Image blurring and unevenness)
It has been found that when θ1 is 20 ° or less and θ1 / θ2 ≦ 0.37 as in the present invention, blurring or unevenness of the image does not occur, but θ1 is 20 ° or more, or 0.37 <θ1. In the case of / θ2, image blurring or unevenness is observed. The reason for this is presumed to be dependent on the state of the ears of the magnetic brush at the development position, similar to the occurrence of white spots.

(Developer clog)
The developer clogging that occurs during development will be described with reference to FIG. FIG. 5A is a cross-sectional view of the development position in a normal state where no developer clogging occurs. FIG. 5B is a cross-sectional view of the development position in a state where developer clogging occurs. As shown in FIG. 5B, the developer clogging means that the developer 80 conveyed by the developing roller at the closest position P between the developing roller 4 and the photosensitive member 1 is transferred between the developing roller and the photosensitive member. This means a state where the developer cannot pass through, stays upstream in the transport direction of the developer, and the developer 80 overflows out of the developing unit.

  Under the conditions of the present invention, the ears of the magnetic brush are standing at the development position, but are inclined to the upstream side in the transport direction, and the magnetic attraction of the magnetic brush is increased by increasing the magnetic attraction force at the development position. The connection force and the attractiveness toward the developing roller become stronger, and the clogging of the developer can be prevented.

  As described above, in the present invention, while emphasizing development efficiency, an effective form for suppressing white spots due to leakage and preventing clogging of the developer can be achieved. Furthermore, the magnetic attraction force at the closest position is 0.27 N or more, thereby realizing a further effect on developer clogging.

The setting of other development conditions such as the development bias is independent of the effect of the present invention related to the magnetic pole arrangement, and the effect of the present invention is produced even if it is arbitrarily set from other requirements. In particular, the conditions in which the effect of the present invention appears remarkably include the developing roller diameter and the magnetic force of the carrier as the developer. As the developing roller becomes smaller in diameter, problems such as leakage are more likely to occur, and therefore the effects of the present invention also become prominent. The developing roller diameter is preferably in the range of φ14 to 18 mm. Similarly, as the saturation magnetization of the carrier increases, the effect of the present invention increases, and 0.72 to 0.77 (10 ⁻⁴ Wb · m / kg) is a preferable range.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

  The developing unit 19 shown in FIGS. 2 and 3 was mounted on the image forming apparatus shown in FIG. 1 to form an image.

In the developing unit 19, the developing roller diameter is φ16 mm. The normal direction magnetic flux density pattern of the developing roller is as shown in FIG. The magnetic flux density values of the magnetic poles are N1: 110 mT, S1: 70 mT, N2: 50 mT, S2: 60 mT, and S3: 55 mT. As for the developing bias, AC was superimposed on DC, Vpp = 1.4 kV, f = 4 kHz, and a rectangular wave was used as the AC waveform. The peripheral speed ratio θ between the developing roller and the photosensitive member is 2.2. As the developer, a highly charged magenta toner (6.5 μm) and a high magnetic force carrier (33 μm, 0.75 × 10 ⁻⁴ Wb · m / kg) were used.

  Any of the following experimental examples is performed under the above-described common experimental conditions except for the conditions shown in each table.

  Table 1 below shows θ1, θ2, θ1 / θ2, and the magnetic attraction force at the position P where the developing roller 4 is closest to the photosensitive member 1 in each experimental example. Experimental Examples 1 to 3 and 11 to 15 are examples in which the magnetic pole arrangement is set according to the present invention, and Experimental Examples 4 to 10 are experimental examples in which the magnetic pole arrangement is set outside the scope of the present invention.

  Table 2 below shows experimental conditions in each experimental example. The condition d is the most unfavorable condition for white spots among the conditions a to d.

  In the items of Table 2, the environment is an environment in which the image forming apparatus is operated, and an image forming experiment was performed in a test room in which the temperature and humidity were adjusted so as to become a normal environment (NN) or a low temperature and low humidity environment (LL). .

  Further, as shown in FIG. 5, Ds is the closest distance between the developing roller 4 and the photoreceptor 1, and Db is the distance between the regulating plate 5 and the developing roller 4 as shown in FIG. This was also adjusted during the experiment. Ds = 0.23 mm and Db = 0.25 mm are the condition settings that can be narrowest in terms of the configuration of the apparatus used, and are advantageous for image density, but are disadvantageous for white spots due to leakage.

  Tc is the toner concentration and represents the amount of toner contained in the developer in units of mass percent. For 6.5% and 9.5%, the lower and upper limits of the normal use range were selected. The transport amount is an actual measurement of the developer transport amount on the developing roller based on these settings.

(Evaluation methods)
Next, an evaluation method and results of each experimental example will be described.

(White spots)
Regarding the occurrence of white spots due to leakage, a solid image was output with A3 paper while changing the DC component of the developing bias for each experimental example in Table 1. The reason for changing the developing bias is to obtain an appropriate density by correcting the influence on the density due to the change of the magnetic pole arrangement. The transmission density of the image sample was measured, a sample with an appropriate density was picked up, and the number of white spots that occurred was counted.

  FIG. 6 and Table 5 below show the results of each experimental example. FIG. 6 is a graph showing the white spot evaluation results for each experimental example in terms of the number of white spots with respect to θ1 / θ2. As already described, it can be seen that the state of the ears of the magnetic brush is controlled by θ1 / θ2, and the presence or absence of white spots is clearly divided.

  When θ1 / θ2 is 0.19 or more, no white spots are generated, and when it is less than 0.19, white spots are rapidly generated. In addition, even when the experimental conditions shown in Table 2 change, the degree of occurrence of vitiligo spots changes, but the threshold value (θ1 / θ2 = 0.19) that divides the presence or absence of occurrence is completely changed. Absent. From this, it can be inferred that this magnetic pole arrangement change has an inherent effect independent of other factors affecting the occurrence of vitiligo spots.

(Solid image evaluation)
Regarding the occurrence of density unevenness and image blurring in a solid image, a solid image is also output for each experimental example in Table 1, and the density, density unevenness, graininess (fineness), etc. of the solid image are visually evaluated. Ranking was performed as a solid image rank.

  Table 3 shows ranking criteria based on visual evaluation of density unevenness and graininess. The solid image rank was determined by combining the visual observation of density unevenness and graininess. The higher the solid image rank, the better the solid image, and the solid image rank R3 or higher where neither density unevenness nor toner deficiency extends over the entire region is the allowable range as the output image.

  FIG. 7 shows the results of each experimental example. FIG. 7 is a graph showing the solid image evaluation results for each experimental example in the solid image rank with respect to θ1 / θ2. When θ1 / θ2 is 0.37 or less, the solid image rank is R3 or more.

  As already mentioned, the solid image quality is better when the magnetic brush is standing, but it is close to the standing state (the ear is not sleeping) until the size of θ1 / θ2 is some extent. ) Can be maintained. That is, it is possible to set a spiked state that can suppress the occurrence of white spots and that has good solid image quality. That is below the threshold value (θ1 / θ2 = 0.37).

(Developer clog)
To prevent clogging of the developer, prepare a plurality of developing rollers with different magnetic attractive forces at the closest positions of the developing roller and the photoconductor, and replace the developing roller for each experimental example in Table 1. A white solid image was output, and the state of the magnetic brush at the upstream position in the rotation direction of the developing roller was visually observed at and near the closest position between the developing roller and the photoconductor immediately thereafter. In addition, a fine line image was also output, and the reproduction state of the fine line was also visually evaluated and ranked as a clogging rank in combination with the state of the magnetic brush.

  Table 4 below shows the criteria for ranking based on the visual evaluation of the state of the magnetic brush and the reproduction state of the thin line. The clogging rank was determined by combining the state of the magnetic brush and the visual evaluation of the thin line. As the clogging rank increases, the occurrence of developer clogging is suppressed, and the clogging rank R3 or higher where neither the tip irregularity nor the fine line blurring extends over the entire area is an allowable range in using the apparatus.

  Table 5 below and FIG. 8 show the results of each experimental example. FIG. 8 is a graph showing the result of evaluation of developer clogging for each experimental example in terms of clogging rank against magnetic attractive force. When the magnetic attractive force is 0.27 N or more, the clogging rank is R3 or more.

  In the experimental example according to the present invention, the closest position between the developing roller and the photosensitive member is located between the S1 pole and the N1 pole. At the closest position, the ears of the magnetic brush are standing, but are inclined to the upstream side in the transport direction. By increasing the magnetic attractive force at this position, the connecting force of the ears of the magnetic brush, and further development Attraction to the roller side becomes strong, and clogging of the developer can be prevented. From the experimental results, it is preferably 0.27N or more, more preferably in the range of 0.27 to 0.37N.

  About the result of a present Example, it can conclude as follows.

  According to the embodiment of the present invention, by appropriately arranging the magnetic poles included in the developer carrier (developing roller), the magnetic force at the closest position (development position) between the image carrier (photosensitive member) and the developer carrier. It was possible to appropriately control the brushing state of the brush, to suppress the white spot image due to the leak, and to form a high-quality image free from image blur and density reduction.

  Furthermore, it is possible to provide an image forming apparatus that can appropriately set the magnetic attraction force of the developer carrying member at the closest position between the developer carrying member and the image carrying member, and is less prone to developer clogging. I was able to.

  There may be many other conditions that affect these effects, but the magnetic pole arrangement of the present invention is particularly dominant and has its own effects independent of other conditions. The set threshold value is dominantly determined by the magnetic pole arrangement regardless of other conditions.

  Therefore, the embodiments of the present invention are not limited to the above-described examples, and there is room for arbitrarily changing other conditions according to various requirements without departing from the spirit of the present invention.

1 is a schematic cross-sectional view illustrating an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a schematic cross-sectional view of the imaging cartridge 17 in FIG. 1. FIG. 3 is an enlarged schematic cross-sectional view illustrating a state in which the photosensitive member 1 is developed by the developing roller 4 in FIG. 2. FIG. 3 is an enlarged view of a magnetic flux density pattern in a normal direction of the developing roller 4 in FIG. 2. It is sectional drawing of the development position which shows the generation | occurrence | production state of a developer clogging. It is a graph which shows the white spot image generation result by the leak (discharge) in the Example of this invention. It is a graph which shows the image evaluation result in the solid image in the Example of this invention. 6 is a graph showing a result of occurrence of developer clogging in an example of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image carrier 2 Cleaner 3 Charging device 4 Developing roller 5 Restriction plate 6 Deviation return member 7 Dust prevention plate 8 Supply screw 9 Stirring screw 10 Developing housing 11 Fixing unit 12 Secondary transfer roller 13 Toner cartridge 14 Primary transfer belt 15 Cleaner Unit 16 Waste toner box 17 Imaging cartridge 18 Exposure device 19 Developing unit 20 Photosensitive drum unit 21 Lower seal 22 Developing tank

Claims (2)

In a developing device that forms a toner image on an image carrier by developing the electrostatic latent image formed on the surface of the image carrier with a two-component developer containing toner and a magnetic material.
A developer carrier for carrying and transporting a two-component developer in a direction opposite to the moving direction of the image carrier;
A developer pole which is encapsulated and fixed to the developer carrier and forms a magnetic brush so that the two-component developer on the developer carrier rubs the surface of the image carrier; A plurality of magnetic poles including a transport pole for transporting the two-component developer to the development pole,
The developing device according to claim 1, wherein the arrangement of the magnetic poles satisfies the following conditions (1), (2), and (3).
(1) The magnetic flux density peak in the normal direction of the developing pole is arranged at a downstream side of 10 ° or more and 20 ° or less with respect to the developer transport direction from the closest position between the developer carrying member and the image carrier.
(2) The magnetic flux density peak in the normal direction of the transport pole is arranged upstream of the closest position.
(3) 0.19 ≦ θ1 / θ2 ≦ 0.37, where θ2 is the angle between the development pole peak and the transport pole peak, and θ1 is the angle between the closest position and the development pole peak. . 2. The developing device according to claim 1, wherein a magnetic attraction force of the developer carrier at a position closest to the developer carrier and the image carrier is 0.27 N or more.

Images